1

Avgas Additives

Lead and Halogen Contamination from Aviation Fuel Additives at Brackett Airfield

Charles Taylor[a]

, Kelly Park[b]

, Kellyann Murphy[c]

, and Teija Mortvedt[d]

Compounds containing lead, chlorine, and bromine are used as anti-

knock fuel additives in aviation gasoline. Their presence in elevated

amounts indicates fuel runoff or particle settlement from combusted

fuel. This study aims to measure the concentration of these

elements in the soil around Brackett Airfield in LaVerne,

California. X-ray fluorescence measurements reveal lead content at

22.1 – 152.2 ppm with an average of 48.0 ± 7.4 ppm; bromine at

2.1 – 42.6 ppm, averaging at 10.0 ± 2.1 ppm; and chlorine at 315.5

– 2567.3 ppm, averaging at 605.2 ± 110 ppm. Atomic absorption

spectroscopy measured lead at 5.9 – 94.8 ppm, averaging at 20.6

± 5.0 ppm. None of the results obtained exceed allowable EPA

standards and therefore should not pose a health risk to

surrounding communities. Further studies are recommended on

soils collected within the airport fence line—contamination is

likely higher due to closer proximity to the runway, fueling

stations, and airplane hangars.

____________

[a] Associate Professor of Chemistry, Pomona College, Claremont,

California E-mail: ctaylor@pomona.edu

[b] Chemistry, Pomona College, Claremont, California E-mail: kelly.park@pomona.edu

[c] EA Chemistry, Pomona College, Claremont, California E-mail: kellyann.murphy@pomona.edu

[d] Chemistry, Joint Science, Claremont, California E-mail: tmortved@scrippscollege.edu

Introduction

Brackett Airfield in LaVerne, California is a small, publicly

owned airfield open to Los Angeles County. The airport is in

continuous operation and provides services to helicopters, military,

and jet aircraft; however, general aviation aircraft make up the

majority of operations based in the field.1 General aviation planes

are of interest because they run on aviation gasoline, or avgas, a

leaded, high-octane fuel. Avgas is used by piston-driven engines

while the larger turbine engines of jet planes run off of a non-

leaded, kerosene-based fuel.

Lead is added to avgas in the form of tetraethyl lead (TEL) in

order to increase the octane rating, a measure of the “knock” inside

engines. Knock describes the tendency for gasoline to

spontaneously ignite, which can cause dangerous pressure and

stress on an engine. Piston engines need a high-octane fuel to

withstand the high power and pressure required of them, especially

during takeoff.2 There is currently no suitable, cost-effective

unleaded fuel option available—thus leaded avgas has remained

standard3 despite the negative health effects of exposure to lead.

Lead is a toxin that targets the nervous system, renal function,

and vascular system. It is responsible for decreased physical and

mental development and capacity, especially in children who are

still maturing. It can also cause high blood pressure, hearing loss,

attention deficit, and more extreme neurological damage, including

short-term memory loss and lowered IQ.4,5

Lead typically enters

the body through digestion or inhalation, and in some cases, skin

contact. Inorganic lead, like the type found in paint, food, plastics,

etc., is not absorbed by the skin. However, tetraethyl lead, which is

still legal for aircraft, watercraft, and farm machinery, may be

absorbed through the skin.4 Once absorbed, lead enters the

bloodstream and circulates throughout the body, making its way

into soft tissue and eventually to bone, where it replaces calcium.

The ability of lead to mimic the role of calcium is a major reason

for its neurological effects: as lead reacts similarly to calcium, it

can compete for binding sites in the cerebellum, ultimately leading

to flaws in neurotransmission.6

The body is able to purge the bloodstream relatively quickly,

the half-life of lead in blood being 35 days. Thus, a blood lead test

is a good indicator of recent exposure. However, bone samples

must be analyzed to evaluate long-term exposure. Although

symptoms may not be recognized, it is established that no toxic

threshold for lead exists; bodily lead contamination at any level has

the potential to interfere with normal activity.7

The Environmental Protection Agency (EPA) estimates that

almost half of all lead emissions in the United States comes from

small aviation aircraft fuel.8 In April 2010, the EPA issued the

Advanced Notice of Proposed Rulemaking (ANPR) on Lead

Emissions from Piston-Engine Aircraft Using Leaded Aviation

Gasoline,5 which was open to public comment until August 28,

2010.9 If the EPA finds in the future that lead emissions from

aircraft contribute to pollution and therefore endanger public health,

the Federal Aviation Administration (FAA) would be required to

establish standards to control lead emissions from piston-engine

aircraft.5

This would place pressure on the development of an

unleaded aviation gasoline.

General aviation aircraft currently runs off of Avgas 100LL.

This gas contains TEL, which acts to form a protective layer on the

soft valve seat of engines to prevent it from fusing to the valve and

being taken from the surface of the seat.2 This, along with other

surface damage, is known as Valve Seat Recession (VSR). The

only way to prevent VSR is to produce harder metal valve seats, a

costly modification for old aircraft, or use VSR additives, which do

not up octane ratings and thus cannot be used for aviation.2

Unleaded fuels are in development, including 82UL in the U.S.,

which is only approved for use on a few engine types. Even so, it is

estimated that only 60% of aircraft world-wide would be able to

use this fuel grade; the rest would need system modifications prior

to approval.2

It is obvious that the transition to unleaded gasoline

will be slow and arduous given current conditions, but there is little

doubt that the unleaded fuel transition will occur at some point in

the future.

Effort to redirect the path of aviation fuel is due in large to

the Clean Air Act. Current National Ambient Air Quality

2

Standards (NAAQS) for lead are set to 0.15 !g/m3 over a rolling

3-month average,10

while soil concentration is set to a standard of

1200 ppm in non-play areas and 400 ppm in play areas.11

Lead emitted from internal combustion engines is usually in

the form of lead halides due to the presence of ethylene dibromide

and ethylene dichloride (EDC), added as scavenging agents12

to

prevent lead deposition inside an engine. EDC is reasonably

anticipated to be a human carcinogen. However, experimental trials

on animals have been inconclusive.13

Chlorine and bromine in their

elemental forms are highly toxic, but these gases would not remain

in soil. It was expected that only the typically harmless chlorides

and bromides would be found. However, a positive correlation of

halogen to lead concentration would support the hypothesis that

contamination is in large part due to leaded gasoline.

We used X-ray fluorescence (XRF) to measure lead and

halogen content, and graphite furnace atomic absorption (AA)

spectroscopy for lead analysis. Employing two different techniques

enabled us to determine the percent extractability of lead in soil

and provide a measure of reproducibility. X-rays penetrate but do

not destroy the entire sample, and the emitted rays analyzed by the

detector are representative of all present elements regardless of

their chemical form. However, the AA method requires the sample

to be digested first by an acid. While hydrofluoric acid would

dissolve the silicates and metal oxides that are present in

environmental samples, safety concerns necessitate the use of nitric

acid instead: thus, some of the lead that remains bound in

complexes will be filtered out and will not contribute to the

concentration measured by AA.

Materials and Methods

Sample collection: A coring sampler was bored into the

ground to a depth of about six inches in order to collect the soil

packed inside. In areas covered with freshly turned dirt or heavy

organic debris, only the lower four to five inches was collected. A

total of 48 samples were taken from the playground near the main

parking lot, areas near hangars, and along the eastern perimeter of

the fence around the field (latitudinal and longitudinal locations

were recorded on a Trimble®

JunoTM

ST handheld GPS unit).

Sample preparation: All samples were filtered in sieves to

eliminate larger rocks and organic material to be dried for up to 12

hours in a 100 °C oven. The dried soil was then powdered using a

steel ball mill.

For analysis by atomic absorption (AA) spectrometry, three

replicates of 0.5 g each per soil sample were digested with 10 mL

of 70% HNO3 and microwaved with recommended EPA settings.14

The remaining soil was filtered out and the remaining solution was

diluted to 25 mL of deionized water. Further dilutions were carried

out using deionized water as needed.

For analysis by X-ray fluorescence (XRF), three replicates of

5 g each per soil sample were mixed with 1 g of cellulose binder.

These were then pressed into 32 mm pellets using SPEX 3630 X-

Press for five minutes of 30 tons and one minute of release.

Sample analysis by AA spectrometry: All samples were

analyzed for lead content with the graphite furnace method in

PerkinElmer AAnalyst 800 after a 1:10 dilution. Three injections

of each sample replicate were measured against a calibration curve

using lead standards of 5, 10, 25, 50, and 100 ppb.

Sample analysis by XRF: Each pressed pellet was analyzed

for lead, chlorine, and bromine using a PANalytical Axios X-Ray

Fluorescence Spectrometer. Lead and bromine levels were

measured based on pre-programmed calibrations on PANalytical’s

ProTrace program. A separate chlorine calibration was created

using standards from U.S. Geological Survey (USGS) BHVO-2

(ultra-pure quartz dilutions of 70%, 50%, 30%, and 10% of a given

150 ppm chlorine concentration), Geological Survey of Japan JMS-

1 (a 10% dilution of 26,900 ppm chlorine), and undiluted USGS

GSP-2 (400 ppm chlorine). A blank of 5 g ultra-pure quartz and 1 g

binder was also incorporated in the calibration.

Statistical and data analysis: Outliers among replicates were

subjected to Dixon’s Q test and rejected accordingly. Remaining

replicates were then averaged and 95% confidence intervals

determined.

All maps were created using ArcGIS software with data

points taken from the handheld GPS unit.

Results and Discussion

Table 1. Lead Concentration (XRF)

Sample Lead Concentration (ppm) 95% C.I.

(ppm)

1 152.2 1.1

2 37.2 1.6

3 29.8 0.91

4 42.4 1.0

5 55.0 1.1

6 22.1 1.9

7 32.5 6.9

8 79.3 1.5

9 116.4 5.7

10 85.8 2.2

11 36.4 2.0

12 42.0 1.1

13 54.6 10.6

14 53.7 5.3

15 26.0 0.95

16 70.4 1.3

17 62.8 0.53

18 86.9 6.4

19 115.7 6.5

20 33.3 1.5

21 27.2 0.65

22 27.6 1.4

23 35.4 3.3

24 36.23 2.1

25 37.1 2.5

26 37.2 2.4

27 26.3 1.9

28 25.2 1.8

29 47.0 1.9

30 52.3 2.7

31 44.4 2.6

32 36.6 5.5

33 47.5 3.5

34 26.3 0.75

35 28.4 1.4

36 45.5 0.71

37 55.0 1.5

38 52.5 4.7

39 41.3 0.64

40 36.1 1.9

41 42.2 2.6

42 39.3 0.79

43 40.7 3.5

44 48.3 1.1

45 33.2 3.4

46 37.3 2.8

47 29.1 0.17

48 34 0.52

Average lead concentration: 48.0 ± 7.4 ppm

3

Table 2. Lead Concentration (AA)

Sample Lead Concentration (ppm) 95% C.I.

(ppm)

1 29.1 1.8

2 12.7 0.72

3 8.9 1.1

4 13.3 1.0

5 19.1 4.6

6 8.9 1.1

7 14.7 3.0

8 38.5 0.59

9 95.0 10.

10 40.8 1.9

11 15.0 0.38

12 22.8 0.61

13 28.9 4.0

14 27.4 3.3

15 13.8 2.0

16 39.7 4.0

17 36.7 1.6

18 46.1 0.72

19 21.0 2.7

20 14.9 0.57

21 12.5 1.6

22 15.3 2.8

23 16.3 0.54

24 17.1 1.4

25 14.0 0.31

26 13.8 0.010

27 9.0 0.41

28 7.9 0.31

29 21.7 8.8

30 17.9 0.74

31 14.4 0.41

32 9.7 0.22

33 18.3 4.5

34 5.9 0.20

35 7.5 0.69

36 12.7 0.79

37 14.6 1.6

38 87.6 130*

39 10.9 0.55

40 8.7 0.92

41 12.5 0.12

42 9.9 0.35

43 12.2 0.15

44 15.6 1.3

45 9.9 0.34

46 10.1 0.010

47 9.0 0.060

48 9.8 0.34

*possible contamination

Average lead concentration: 20.6 ± 5.0 ppm

Table 3. Extractability (Lead)

Sample ppm (AA) ppm

(XRF) % Extraction

1 29.1 152.2 19.1%

2 12.7 37.2 34.0%

3 8.9 29.8 29.8%

4 13.3 42.4 31.4%

5 19.1 55.0 34.8%

6 8.9 22.1 40.1%

7 14.7 32.5 45.4%

8 38.5 79.3 48.6%

9 95.0 116.4 81.6%

10 40.8 85.8 47.6%

11 15.0 36.4 41.3%

12 22.8 42.0 54.3%

13 28.9 54.6 52.9%

14 27.4 53.7 51.0%

15 13.8 26.0 53.3%

16 39.7 70.4 56.3%

17 36.7 62.8 58.4%

18 46.1 86.9 53.0%

19 21.0 115.7 18.2%

20 14.9 33.3 44.7%

21 12.5 27.2 45.7%

22 15.3 27.6 55.4%

23 16.3 35.4 46.0%

24 17.1 36.2 47.2%

25 14.0 37.1 37.7%

26 13.8 37.2 37.1%

27 9.0 26.3 34.4%

28 7.9 25.2 31.4%

29 21.7 47.0 46.1%

30 17.9 52.3 34.3%

31 14.4 44.4 32.5%

32 9.7 36.6 26.5%

33 18.3 47.5 38.4%

34 5.9 26.3 22.4%

35 7.5 28.4 26.5%

36 12.7 45.5 27.9%

37 14.6 55.0 26.6%

38 87.6 52.5 167.0%*

39 10.9 41.3 26.5%

40 8.7 36.1 24.1%

41 12.5 42.2 29.6%

42 9.9 39.3 25.2%

43 12.2 40.7 29.9%

44 15.6 48.3 32.3%

45 9.9 33.2 29.7%

46 10.1 37.3 27.0%

47 9.0 29.1 30.8%

48 9.8 34.0 28.7%

*possible contamination

Average extractability: 40.9% ± 6.3%

4

Table 4. Bromine Concentration (XRF)

Sample Bromine Concentration (ppm) 95% C.I.

(ppm)

1 22.0 1.2

2 24.6 0.49

3 42.6 0.35

4 16.7 0.24

5 16.4 0.41

6 3.8 0.13

7 2.1 1.4

8 8.8 0.57

9 6.5 1.1

10 9.7 0.20

11 23.8 0.75

12 2.2 1.6

13 6.0 1.3

14 4.9 0.73

15 2.4 1.1

16 9.7 0.63

17 6.2 0.17

18 6.5 0.070

19 7.6 0.52

20 14.2 0.26

21 6.2 0.11

22 6.5 0.77

23 7.3 0.41

24 8.0 0.69

25 5.2 0.35

26 3.3 0.36

27 14.4 1.1

28 4.9 0.33

29 5.7 0.59

30 5.4 0.73

31 7.1 0.34

32 17.2 0.35

33 7.4 0.60

34 15.8 0.40

35 10.6 0.23

36 14.9 0.56

37 19.8 0.74

38 10.8 0.24

39 14.5 0.75

40 9.8 0.41

41 7.7 0.00

42 8.0 0.35

43 6.3 1.4

44 5.5 1.3

45 4.9 0.13

46 7.5 0.57

47 4.0 1.3

48 6.6 0.33

Average bromine concentration: 10.0 ± 2.1 ppm

Table 5. Chlorine Concentration (XRF)

Sample Chlorine Concentration (ppm) 95% C.I.

(ppm)

1 525.7 26

2 532.9 2.9

3 650.3 12

4 430.9 30.

5 428.4 21

6 392.1 14

7 645.4 12

8 365.9 2.9

9 653.7 8.6

10 523.2 17

11 1312.6 43

12 447.0 83

13 527.7 45

14 548.6 8.1

15 363.8 21

16 340.8 5.3

17 346.7 22

18 509.2 48

19 534.1 11

20 2567.3 28

21 315.5 24

22 388.8 20

23 408.6 6.8

24 344.3 18

25 362.3 16

26 372.4 8.6

27 360.5 15

28 433.8 36

29 579.0 9.5

30 467.0 17

31 572.5 6.7

32 1028.0 40

33 451.3 11

34 460.4 29

35 652.0 15

36 491.1 13

37 1094.5 19

38 488.3 6.3

39 1078.3 30

40 710.9 12

41 483.4 9.7

42 903.5 24

43 477.8 29

44 597.6 11

45 462.8 29

46 1262.6 38

47 416.4 18

48 741.0 29

Average chlorine concentration: 610 ± 110 ppm

5

Figure 1. Spatial distribution of lead concentrations in ppm given by XRF analysis.

Fueling Station

Figure 2. Spatial distribution of lead concentrations in ppm given by AA spectroscopy.

Fueling Station

6

Figure 3. Spatial distribution of bromine concentrations in ppm given by XRF analysis.

Fueling Station

Figure 4. Spatial distribution of chlorine concentrations in ppm given by XRF analysis.

Fueling Station

7

_______________________

Soil samples were analyzed for lead using X-ray

fluorescence (XRF) and atomic absorption spectroscopy (AA).

XRF results showed lead concentrations ranging from 22.1 – 152.2

ppm with an average of 48.0 ± 7.4 ppm (Table 1, Fig. 1). AA

results showed lead concentrations ranging from 5.9 – 94.8 ppm,

averaging at 20.6 ± 5.0 ppm (Table 2, Figure 2). While XRF is

able to measure the total lead concentration in each sample, AA is

only able to measure the portion of lead that is extractable. On

average, 40.9% ± 6.3% of the lead in the samples is extractable

under the given sample preparation conditions (Table 3). There

was one sample (Sample 38) in which AA yielded a higher

concentration than XRF, giving a value of >100% extractability.

The lead concentration given by AA for this sample had a very

large confidence interval, which included zero. This is likely due

to contamination of replicates.

XRF analysis was used to measure both the chlorine and

bromine concentrations in the soil samples. Bromine levels ranged

from 2.1 – 42.6 ppm, averaging at 10.0 ± 2.1 ppm (Table 4, Fig. 3).

Chlorine levels ranged from 315.5 – 2567.3 ppm, averaging at

605.2 ± 110 ppm (Table 5, Fig. 4). There is no correlation between

lead concentration and total halogen concentration in the soil

samples (R2 = .0069, Fig. 5).

Conclusions

None of the soil samples had concentrations of lead

exceeding EPA standards and therefore should not pose a health

risk to the surrounding community. This sample set, however, is

limited to the southeast perimeter and public parking lot of the

airport. Contamination is likely to be higher inside the airport

fence line and closer to the runway, fueling stations, and airplane

hangars. While the surrounding community may not be at risk, the

people who work at and use the airport may be.

The samples with the highest observed lead concentrations

tend to be from the west side of the airport, where the fueling

station and many airplane hangars are located. This can be

accounted for by pilots checking or emptying fuel tanks as well as

by actual fueling. The eastern fence line, located behind the

runway, carries moderate levels of lead content. Engine power, and

therefore pollutant emissions, is highest during takeoff and

climbout, explaining the elevated lead concentrations behind the

runway.15

The southeast corner at the bottom of the map presents

the smallest amount of lead contamination. This area is relatively

distant from the runway, fueling station, and hangars, thus

providing little opportunity for contamination.

While there is no correlation between the lead concentration

and total halogen concentration between each sample, roughly

similar deposition patterns may be observed by looking at the

maps, particularly in the chlorine map. The bottom southeast

corner of the airport has very little contamination, while the west

and east sides have higher concentrations, which suggests that the

source of these halogens is, in fact, the avgas. Differences in lead

and halogen concentrations in the soil may be due to differences in

mobility and reactivity of the species in this environment: when

lead halides are exposed to sunlight, photolysis occurs and releases

free halogens into the air, while the lead remains in the soil.16

If

certain areas of the airport receive more sunlight than others, such

as the open field, halogens will be more readily released and their

concentrations in the soil will differ.

It is recommended that further research be conducted inside

the perimeter of the airfield. In addition, soil contamination is only

one facet of the impact of avgas emission; studies performed on air

quality around airports indicate elevated levels of harmful

pollutants such as ultrafine particles,17

while combustion of

aviation fuel contributes to rising levels of greenhouse gases.18

Figure 5. Regression of lead concentration vs. total halogen concentration. Lead XRF data was used to avoid

differences in concentration due to different extractabilities of the lead compounds. Total halogen concentration was

obtained by adding chlorine and bromine concentrations.

8

Acknowledgments

We would like to thank the Mellon Environmental Analysis

Fellowship and the Rose Hills Foundation for funding this project.

We would also like to thank Professor Charles Taylor for all of his

help and guidance during this project, Professor Katie Purvis-

Roberts for her guidance, Professor Jade Star Lackey and Lee

Finley-Blasi for their instruction on sample prep and use of the

XRF, and Warren Roberts for his help with the GPS units and GIS

software.

____________________

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